Research On Proactive Eavesdropping Technology Based On Wireless Cooperative Relay

The development of wireless communication not only brings great convenience to human society,but also emerges new challenges to public safety.On the one hand,with the rise of wireless services,such as fingerprint recognition and mobile payment,wireless networks are vulnerable to attacks and eavesdropping by illegal users,due to the openness of the transmission medium of wireless networks.On the other hand,wireless technology can also be used by illegal users to commit crimes,violence,and other terrorist actions,which threatens public safety.Therefore,ensuring the safety and reliability of wireless communication networks has become an important part of the construction of communication networks.Proactive eavesdropping technology plays an increasingly significant role in preventing the potential threat from happening,and has become a research hotspot in the field of the physical layer security technology in recent years.Aiming at the problem of potentially suspicious users using wireless networks for criminal activities,the proactive eavesdropping systems based on wireless cooperative relay are studied in the dissertation,and the main research contents are as follows:(1)For the scenario with a single pair of suspicious users pair exists,the proactive eavesdropping scheme of multi-antenna decode-and-forward(DF)assisted relay is studied.Specifically,the eavesdropping relay,which operates in a full-duplex(FD)mode,listens to the suspicious transmitter,and decodes its information,and then forwards the re-encoded information to the legitimate monitor.At the same time,jamming signal is sent to suspicious link by eavesdropping relay to weaken the security threat of suspicious users.Aiming to improve the eavesdropping performance of legal surveillance systems,and reduce the quality of suspicious communication,the suspicious secrecy rate is used as a performance metric in the paper.(2)The optimal legal relay beamforming and power allocation strategy are designed.To obtain the closed expression of the non-convex problem,a two-step optimization strategy is proposed,and the closed expressions of beamforming and power allocation ratio are obtained.In this strategy,the optimal beamforming vector under a given power allocation ratio is first designed,and then the optimal power allocation ratio is derived.The numerical results show that the proposed scheme with optimized multi-antenna relayassisted proactive eavesdropping achieves better performance than the conventional schemes.(3)For the presence of multiple pairs of suspicious users,an unmanned aerial vehicle(UAV)-assisted relay proactive eavesdropping scheme is proposed,with the goal of minimizing the suspicious secrecy rate.The purpose of the UAV is to intercept suspicious information from multiple suspicious links,and to amplify and forward the suspicious information to the legitimate monitor.The UAV-assisted relay is adjusted to its position and power allocation to minimize the suspicious secrecy rate,since UAVs have the advantages of flexibility,high maneuverability and rapid deployment.(4)The position of the relay and the forwarding power for the relay are jointly optimized,where the interference signal is sent by the UAV to weaken the signal-tointerference-to-noise ratio of the suspect receiver,and the position is optimized to attain more effective monitoring,by exploiting the flexibility of the UAV.Since the target problem is non-convex,an iterative algorithm for optimizing the position and forwarding power of the UAV is proposed.First,the optimization variables are divided into two blocks: UAV position and forwarding power.In each of the next steps,one variable block is kept fixed and the other variable is optimized,and then alternately optimized,until the acceptable performance accuracy error is reached.Next,the convergence of the algorithm is verified.Finally,the simulation results show that,compared with the reference scheme,the proposed joint optimization scheme of UAV position and forwarding power has much better eavesdropping performance.